Vertical distribution of Aedes mosquitoes in multiple storey buildings in Selangor and Kuala Lumpur, Malaysia

Transcription

1 University of Malaya From the SelectedWorks of Chen Chee Dhang 2013 Vertical distribution of Aedes mosquitoes in multiple storey buildings in Selangor and Kuala Lumpur, Malaysia Chen Chee Dhang, University of Malaya Available at:

2 Tropical Biomedicine 30(1): (2013) Vertical distribution of Aedes mosquitoes in multiple storey buildings in Selangor and Kuala Lumpur, Malaysia Lau, K.W. 1, Chen, C.D. 1*, Lee, H.L. 2, Izzul, A.A. 1, Asri-Isa, M. 1, Zulfadli, M. 1 and Sofian-Azirun, M. 1 1 Institute of Biological Sciences, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia 2 Medical Entomology Unit, WHO Collaborating Center for Vectors, Institute for Medical Research, Jalan Pahang, Kuala Lumpur, Malaysia * Corresponding author: zidannchris@yahoo.com, chen_ctbr@um.edu.my Received 19 March 2012; received in revised form 30 June 2012; accepted 9 November 2012 Abstract. The aim of the present study was to determine the vertical distribution and abundance of Aedes mosquitoes in multiple storey buildings in Selangor and Kuala Lumpur, Malaysia. Ovitrap surveillance was conducted for 4 continuous weeks in multiple storey buildings in 4 residential areas located in Selangor [Kg. Baiduri (KB)] and Kuala Lumpur [Student Hostel of University of Malaya (UM), Kg. Kerinchi (KK) and Hang Tuah (HT)]. The results implied that Aedes mosquitoes could be found from ground floor to highest floor of multiple storey buildings and data from different elevation did not show significant difference. Ovitrap index for UM, KB, HT and KK ranged from %, %, % and % respectively. Aedes aegypti and Aedes albopictus were found breeding in HT, KK and KB; while only Ae. albopictus was obtained from UM. The results indicate that the invasion of Aedes mosquitoes in high-rise apartments could facilitate the transmission of dengue virus and new approaches to vector control in this type of residential area should be developed. INTRODUCTION Mosquito-borne diseases such as dengue haemorrhagic fever and dengue fever (DF) are the most important arthropod-borne viral diseases of public health in Malaysia. In the year 2011, a total of 19,884 DF cases were reported with 36 deaths in Malaysia (Ministry of Health Malaysia, 2011). Aedes aegypti and Aedes albopictus are the two major vectors involved in these infections. (Lam, 1993; Chen et al., 2005a). Aedes aegypti is a domestic mosquito in urban areas exclusively breed in artificial containers such as earthen jars and plastic containers which contain relatively clear water near human dwellings (Hasanuddin et al., 1997), while Ae. albopictus was reported breeding in artificial containers and natural containers near human dwellings (Hawley, 1988). Both species are adapted to urban and suburban areas (Chen et al., 2006). The close association between human and Aedes mosquitoes has provided the mosquitoes with breeding sites, shelter, and blood meals, which can increase the risk of dengue transmission. Ovitrap surveillance is the commonest sampling method to monitor Aedes mosquitoes populations (Service, 1992; Cheng et al., 1982). According to Lee (1992b), ovitrap surveillance has been shown to be a more effective and sensitive technique especially when the Aedes infestation rates were low. Many studies had been done in Malaysia to determine the population and abundance of Aedes mosquitoes (Lee, 1992a, 1992b; Chen et al., 2005b, 2006; Rozilawati et al., 2007; Wan-Norafikah et al., 2009). However, little information is available on the distribution of Aedes mosquitoes at different 36

3 level of high-rise buildings. A preliminary study on the vertical dispersal of Aedes population in high-rise apartments was conducted by Wan-Norafikah et al. (2010) in Putrajaya. Their study indicated the possibility of lower Aedes population to be found at higher level of high-rise apartments. However, their study was conducted in highrise apartments with 10 levels in one study site only. The present study was conducted in highrise apartments located in 4 selected urban residential areas in Kuala Lumpur and Selangor. This study provides more comprehensive information regarding the vertical distribution and abundance of Aedes mosquitoes in high-rise apartments in Kuala Lumpur and Selangor, Malaysia. Furthermore, this work explains the extent of Ae. aegypti and Ae. albopictus co-habitation in vertically distributed breeding sites. MATERIALS AND METHODS Description of study sites Ovitrap surveillance was conducted in highrise apartments located in 4 residential areas namely, Kg. Baiduri (KB), Student Hostel s University of Malaya (UM), Kg. Kerinchi (KK) and Hang Tuah (HT). The geographical and ecological description of the study sites are given in Table 1. Table 1. Geographical and ecological description of study sites Study site Geographical Description Physical Description Ecological Description 12 th Student College, University of Malaya (UM) 3 07 N, E Located in Kuala Lumpur The building consists of 9 floors. 34 units of rooms each floor. Each floor is about 3.0 meter in height. The building is about 10 years old. High vegetation in the study site. Tree and shrubs planted around the student college. The environment is generally clean and well managed. Vista Angkasa Apartment, Kampung Kerinchi (KK) 3 06 N, E Located in Kuala Lumpur near the border of Selangor state. The building consists of 15 floors. 10 units of houses each floor. Level height is 3.0 meter. The building is about 15 years old. Scattered vegetation around the apartment. Proper waste management and drainage system. Sri Sarawak Apartment, Hang Tuah (HT) 3 08 N, E Located in the city center of Kuala Lumpur. The building consists of 16 floors. 16 units of houses each floor. Level height is 3.0 meter. The building is more than 20 years old. Sparse vegetation and artificial pond around the apartment. Poor waste manage-ment and sanitation. Some of the households have ornamental plants placed around the corridor in front of their house. Impian Baiduri Apartment, Kampung Baiduri (KB) 3 05 N, E Located in Selangor. The building consists of 16 floors. 20 units of houses each floor. Each floor is about 3.0 meter in height. The building is about 3 years old. Scatted vegetation around the building. Proper waste management and drainage system. 37

4 Ovitrap surveillance Ovitrap as described by Lee (1992a) was used in this study. The ovitrap consists of 300 ml plastic container with straight, slightly tapered sides. The opening measures 7.8 cm in diameter, the base diameter is 6.5 cm, and the container is 9.0 cm in height. The outer wall of the container is coated with a layer of black oil paint. An oviposition paddle made from hardboard with measurement of 10.0 cm (Length) x 2.5 cm (Width) x 0.3 cm (Thick) was placed diagonally into each ovitrap which was filled with tap water to the level of 5.5 cm. Ovitraps were placed randomly in each floor of the apartment from ground level to highest level. Ovitraps were placed in not less than 10% of the rooms/houses in each level of the apartments in all study sites. Ovitraps were placed indoor along corridor near stairways, nearby the ornamental plants and under the shoe rack. In this study, indoors refers to the interior of the apartments (Wan- Norafikah et al., 2010). All ovitraps were collected after 5 days and replaced with fresh ovitraps and paddles. Four continuous weekly ovitrap surveillance was conducted in UM and HT, except for KK and KB, where only three collections were made. Identification of larvae The collected ovitraps were brought back to laboratory and the contents were poured into plastic container, together with the paddle. Fresh water was added into the container and a small piece (10 mm) of fresh beef liver was added as larval food. The larvae were allowed to hatch and colonize in the laboratory for another 9 days. The hatched larvae were subsequently counted and identified at 3 rd instar. The larval numbers were recorded individually for each positive ovitrap. Data analysis All data obtained from this study was analysed as follow: 1. Ovitrap Index (OI), the percentage of positive ovitrap against the total number of ovitraps recovered from each site. 2. Mean number of Ae. aegypti and/or Ae. albopictus larvae per recovered ovitrap. All levels of statistical significance were determined at P<0.05 by using the statistical programme, student t-test and one-way ANOVA (SPSS v 11.5). The linear regression analysis (SPSS v 11.5) was conducted to determine the correlation coefficient between OI and level of high-rise apartment. The associations between mean number of larvae per ovitrap and level of high-rise apartment were assessed by spearman rankorder correlation (SPSS v 11.5). RESULTS Table 2 shows the ovitrp index (OI) and the mean number of larvae per ovitrap of Ae. aegypti and Ae. albopictus obtained from ovitrap surveillance conducted in 4 high-rise apartments located in Kuala Lumpur and Selangor. The highest ovitrap index was obtained from Hang Tuah (HT) (45.08%), followed by Kg. Kerinchi (KK) (37.48%), Kg. Baiduri (KB) (21.43%) and University of Malaya (UM) (11.43%). There was significant difference between OI obtained from apartments in all study sites (P < 0.05). The mean number of Ae. aegypti larvae per ovitrap obtained form HT (9.26 ± 0.93) was significant higher than KK (6.20 ± 3.21) and KB (2.64 ± 0.42). There was no Ae. aegypti reported in UM. On the other hand, UM (1.50 ± 0.57) had higher mean number of Ae. albopictus larvae per ovitrap than KK (0.55 ± 0.27), HT (0.30 ± 0.11) and KB (0.24 ± 0.13), but this was not significantly different (P > 0.05). Ovitrap index of each level in all apartments. Aedes were found breeding from ground floor to highest floor in KK and HT. Two out of 9 floors and 6 out of 16 floors in apartments located in UM and KB showed no Aedes breeding, respectively. However, there was no significant difference of OI in each floor within the apartment (P > 0.05) (Figure 1). The OI obtained from KK, HT, KB and UM ranged from %, %, % and %, respectively. The mean numbers of larvae per ovitrap of Ae. aegypti and Ae. albopictus obtained from ovitrap surveillance in each floor in 4 high-rise apartments are shown in 38

5 Table 2. Comparative ovitrap index (mean ± S.E.) and larval number (mean ± S.E.) per ovitrap obtained from four high-rise apartments located in Kuala Lumpur and Selangor, Malaysia Site No. of No. of Ovitrap Collected Larvae Comparison Ovitrap collected Index of the mean Surveillance ovitrap (%) Aedes aegypti Aedes albopictus Ae. aegypti : number larvae conducted Ae. albopictus per ovitrap of Total Mean Total Mean in the Ae. aegypti & number number number number population Ae. albopictus of % of larvae of % of larvae within the larvae per larvae per study site ovitrap ovitrap University of / ± ± ± : 1 T = Malaya (UM) P = Kg. Kerinchi (KK) / ± ± ± : 1 T = P = Hang Tuah (HT) / ± ± ± : 1 T = P = Kg. Baiduri (KB) / ± ± ± : 1 T = P = One way ANOVA F = 3.98 F = F = 2.84 P = P = P =

6 Figure 1. Relationship between ovitrap index (%) and level of four high-rise apartments located in (a) University of Malaya (UM), (b) Kg. Kerinchi (KK), (c) Hang Tuah (HT), and (d) Kg. Baiduri (KB) Table 3. These data indicated that Ae. aegypti was significantly dominant than Ae. albopictus for HT, KK and KB (P < 0.05) by 11 to 31 times. In contrast, Ae. albopictus was the only principal dengue vector found in UM. The mean number larvae per ovitrap of Ae. albopictus obtained from UM, KB, KK and HT ranged from , , and , respectively. On the other hand, mean number larvae per ovitrap of Ae. aegypti obtained from KK, HT and KB ranged from , and , respectively. Generally, Ae. aegypti was found breeding up to the highest floor (16th floor, m), while Ae. albopictus was only up to fourteenth floor ( m). Although the highest mean number of larvae were found in first level of each apartment, there was no significant correlation between the mean number of Aedes larvae collected with the height of the apartment (UM: r = , P = 0.193; KK: r = , P = 0.893; KB: r = , P = 0.263) except HT (r = , P = 0.004), indicating that Aedes could be found breeding in every level of the apartment and not restricted by the height of the apartment. Table 4 shows the percentage and ratio of Ae. aegypti and Ae. albopictus mixed breeding in ovitrap surveillance conducted in high-rise apartments in Kuala Lumpur and Selangor. The percentage of mixed breeding in HT, KB and KK accounted for 10.77%, 15.00% and 26.56% from the total collected ovitraps, respectively. In addition, the number of Ae. aegypti larvae found in mixed breeding ovitrap were folds more that Ae. albopictus. 40

7 Table 3. Mean number of larvae (mean ± S.E.) per ovitrap obtained from four high-rise apartments located in Kuala Lumpur and Selangor, Malaysia University of Malaya (UM), Kg Kerinchi (KK), Hang Tuah (HT), Kg. Baiduri (KB), Kuala Lumpur Kuala Lumpur Kuala Lumpur Selangor Level Height (m) Ae. aegypti Ae. albopictus Aedes sp* Ae. aegypti Ae. albopictus Aedes sp* Ae. aegypti Ae. albopictus Aedes sp* Ae. aegypti Ae. albopictus Aedes sp* ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.67 Spearman s rank r = r = r = r = correlation P = P = P = P = *Mean number of Ae. aegypti and Ae. albopictus larvae per ovitrap 41

8 Table 4. Mixed breeding of Ae. aegypti and Ae. albopictus No. Ovitrap Percentage of positive ovitrap (%) No. of Total no. with mixed Study site collected positive breeding of Mixed breeding ovitrap ovitrap Ae. aegypti of Ae. aegypti and Ae. aegypti Ae. albopictus and Ae. albopictus only only Ae. albopictus Ratio of Ae. aegypti : Ae. albopictus in mixed breeding University of Malaya, Kuala Lumpur Nil Kg. Kerinchi, Kuala Lumur : 1.00 Hang Tuah, Kuala Lumpur : 1.00 Kg. Baiduri, Selangor : 1.00 DISCUSSION According to Tham (2000), ovitrap surveillance is to obtain information on Aedes larval densities in terms of time and space to determine the major breeding sources as well as early forecast of impending outbreaks of dengue. Among the four highrise apartments, HT showed significantly higher OI than other apartment buildings. However, the mean numbers of larvae in each ovitrap were less than 10. This phenomenon may due to avoidance of superoviposion by female as reported by Chadee et al. (1988). In other words, the female mosquitoes preferred to lay eggs in ovitraps having small number of pre-existing eggs to ensure the survival of their progeny (Williams et al., 2008). There was significant difference between the number of larvae per ovitrap of Ae. aegypti and Ae. albopictus obtained from 4 apartments (Table 2). Aedes aegypti population was dominant in KB, KK and HT and these results were similarly reported by Lee (1992a) and Chen et al. (2006) in Aedes surveillance conducted in Selangor state. Aedes aegypti is a domestic mosquito in urban areas and in Malaysia breeds exclusively in artificial containers such as jars, drums and small discarded containers containing relatively clean water near human dwellings (Hasanuddin et al., 1997). The present results suggest that the high-rise apartment creates a complete ecosystem and provide an ecological niche with biotic and abiotic components. Biotic components comprised humans, plants and pet animal in houses, while abiotic factors are temperature, humidity and house structure. Collectively, all the components provide blood meals, water for aquatic stage in house with aquatic plant or unclean rubbish and resting place for adults at various elevations in high-rise apartment. Chadee (2004) reported that the adaptive quality of Ae. aegypti to house design had improved from ground floor to higher elevation apartment buildings. Tinker (1974) suggested that the movement of Ae. aegypti above the ground level may result from the insecticide pressure on breeding sites at ground level. Aedes albopictus was dominant in UM, similarly reported by Wan-Norafikah et al. (2009) and Chen et al. (2009). The typical habitats for Ae. albopictus to breed are natural containers, tree holes and bamboo stumps near human dwellings (Foo et al., 1985; Hawley, 1988). Rudnick et al. (1986) reported that Ae. albopictus has a preference for forest-fringe habitats and well-vegetated habitats with trees. Similarly, in this study the 12 th Residential College was surrounded by trees and other vegetation. The absence of Ae. aegypti in UM may be due to the lack of preferred breeding condition. The environment of 12 th Residential College was generally clean with minimal potable containers since piped water supply is also available. In Table 3, the results showed that Ae. aegypti can be found in highest floor in KB, KK and HT and Ae. albopictus in UM. The 42

9 highest building in this study is HT which is 16 floors in height ( m). The results suggested that Aedes mosquitoes could have been transported by human either by way of elevators or stairs. These results were similar to a study by Liew & Curtis (2004) who reported that ovitraps with rubidium (Rb - ) marked eggs of Ae. aegypti and Ae. albopictus recovered from third level until twenty first level (60.0 m) while Chadee (2004) reported Ae. aegypti can be found in high-rise apartment up to 60.0 m. Among 4 high-rise apartments, the waste management and sanitation status of HT is poor compared to other apartments. Rubbish can be seen everywhere and the dumpsite was improper where the rubbish were placed outside instead inside the big container. Moreover, the drainage system of the apartment was poor where stagnant water accumulated in corridors and in the drain after raining which can provide breeding site for Aedes mosquitoes. This was supported by Chen et al. (2005), who reported that drainage system with stagnant water served as a good artificial breeding site for Aedes mosquitoes. According to Knudsen & Slooff (1992), garbage collection services and surfacewater drainage system combined to create favourable habitat for vectors and may lead to vector-borne disease outbreak. This support the finding that HT obtained the highest OI compared to other apartment, while UM is generally clean with minimal natural container which leads to low OI. Ho et al. (2004) in Hong Kong reported that cleanliness is among the eight key environmental qualities that contributed to good health and hygienic apartment which subsequently guarantee occupants health. Ho et al. (2004) also stated that unhygienic environment not only created nuisance to occupants, but was also conducive to pest problem and growth of micro-organism, which led to infectious diseases outbreak. In conclusion, this study confirmed that ovitrap surveillance is still a reliable and sensitive tool for detecting the presence of dengue vectors. This study showed that the Aedes mosquitoes had invaded and adapted to the high-rise ecosystem and this invasion can enhance the transmission of dengue especially when little or no vector control effort is conducted at the higher elevations. Integrated vector management (IVM) comprising surveillance, source reduction, education and public awareness, biological control, chemical control as well as personal protection should be carried out to suppress the Aedes populations, especially when the ovitrap index is 10% or higher (Lee, 1992b). In Trinidad, West Indies, Chadee (1988) reported that for security reasons, many apartments are closed for most parts of the day and vector control is difficult to execute. This phenomenon also can be seen in Malaysia. Thus, the IVM should be developed to educate households on the potential breeding sites around the high-rise apartment as well as suitable vector control measures in order to prevent future threats of dengue transmission. To prevent breeding of Aedes, operations and maintenance are crucial. Operations refers to standards of cleaning, pest control and refuse handling conditions, whereas maintenance refers to the inspection and maintenance of various building service such as water supply and drainage system. Acknowledgments. The authors thank the University of Malaya for funding this study (PPP, Project No: PS194/2009A and UMRG, Project No: RG034/09SUS). This study is part of the MSc. Thesis of the first author, University of Malaya (UM), Kuala Lumpur, Malaysia. REFERENCES Chadee, D.D. (1988). Effects of closed houses on the Aedes aegypti eradication programme in Trinidad. Medical and Veterinary Entomology 2: Chadee, D.D. (2004). Obsevations on the seasonal prevalence and vertical distribution patterns of oviposition by Aedes aegypti (L.) (Diptera: Culicidae) in urban high-rise apartments in Trinidad, West Indies. Journal of Vector Ecology 29(2):

10 Chen, C.D. (2006). The surveillance and resistance status of the dengue vectors, Aedes (Stegomyia) aegypit (L.) and Aedes (Stegomyia) albopictus Skuse against temephos in Kuala Lumpur and Selangor, Malaysia. M. Sc. Thesis of University of Malaya, Malaysia. Chen, C.D., Nazni, W.A., Lee, H.L. & Sofian- Azirun, M. (2005a). Weekly variation on susceptibility status of Aedes mosquitoes against temephos in Selangor, Malaysia. Tropical Biomedicine 22(2): Chen, C.D., Seleena, B., Mohd Masri, S., Chiang, Y.F., Lee, H.L., Nazni, W.A. & Sofian-Azirun, M. (2005b). Dengue vector surveillance in urban residential and settlement areas in Selangor, Malaysia. Tropical Biomedicine 22(1): Chen, C.D., Nazni, W.A., Lee, H.L., Seleena, B., Mohd Masri, S., Chiang, Y.F. & Sofian- Azirun, M. (2006). Mixed breeding of Aedes aegypti (L.) and Aedes albopictus Skuse in four dengue endermic areas in Kuala Lumpur and Selangor, Malaysia. Tropical Biomedicine 23(2): Chen, C.D., Lee, H.L., Stella-Wong, S.P., Lau, K.W. & Sofian-Azirun, M. (2009). Container survey of mosquito breeding sites in a university campus in Kuala Lumpur, Malaysia. Dengue Bulletin 33: Cheng, M.L., Ho, B.C., Bartnett, R.E. & Goodwin, N. (1982). Role of a modified ovitrap in the control of Aedes aegypti in Houston, Texas, USA. Bulletin WHO 60: Foo, L.C., Lim, T.W., Lee, H.L. & Fang, R. (1985). Rainfall, abundance of Aedes aegypti and dengue infection in Selangor, Malaysia. Southeast Asian Journal of Tropical Medicine and Public Health 16(4): Hasanuddin, I., Miyagi, I., Toma, T. & Kamimura, K. (1997). Breeding habitats of Aedes aegypti (L.) and Aedes albopictus (Skuse) in villages of Barru, South Sulawesi, Indonesia. Southeast Asian Journal of Tropical Medicine and Public Health 28 (4): Hawley, W.A. (1988). The biology of Aedes albopictus. Journal of American Mosquito Control Association 4: Ho, D.C.W., Leung, H.F., Wong, S.K., Cheung, A.K.C., Lau, S.S.Y., Wong, W.S., Lung, D.P.Y. & Chau, K.W. (2004). Assessing the health and hygiene performance of apartment buildings. Facilities 22(3): Knudsen, A.B. & Slooff, R. (1992). Vectorborne disease problems in rapid urbanization: new approaches to vector control. Bulletin of the World Health Organization 70(1): 1 6. Lam, S.K. (1993). Two decades of dengue in Malaysia. Tropical Biomedicine 10: Lee, H.L. (1992a). Aedes ovitrap and larval survey in several suburban community in Selangor, Malaysia. Mosuqito Borne Disease Bulletin 9(1): Lee, H.L. (1992b). Sequential sampling: Its application in ovitrap surveillance of Aedes (Diptera: Culicidae) in Selangor, Malaysia. Tropical Biomedicine 9: Liew, C. & Curtis, C.F. (2004). Horizontal and vertical dispersal of dengue vector mosquitoes, Aedes aegypti and Aedes albopictus, in Singapore. Medical and Veterinary Entomology 18: Ministry of Health Malaysia. (2011). Situasi semasa deman denggi di Malaysia bagi minggu 52/2011. Kenyataan Akhbar Ketua Pengarah Kesihatan Malaysia. pp Rozilawati, H., Zairi, J. & Adanan, C.R. (2007). Seasonal abundance of Aedes albopictus in selected urban and suburban areas in Penang, Malaysia. Tropical Biomedicine 24(1): Rudnick, A., Marchette, R., Garcia, R. & MacVean, D.W. (1986). Dengue virus ecology in Malaysia the general survey, In: Rudnick, A. and Lim, T.W. (Eds.), Dengue fever studies in Malaysia (59 75). Institute for Medical Research, Malaysia. 44

11 Service, M.W. (1992). Importance of ecology in Aedes aegypti control. Southeast Asian Journal of Tropical Medicine and Public Health 23: Tham, A.S. (2000). Surveillance of mosquitoes. In: Mosquitoes and mosquito-borne disease (ed. F.S.P. Ng and H.S. Yong). pp Tinker, M.E. (1974). Aedes aegypti larva habitats in Surinam. Bulletin of the Pan American Health Organization 8(4): Wan-Norafikah, O., Chen, C.D., Soh, H.N., Lee, H.L., Nazni, W.A. & Sofian-Azirun, M. (2009). Surveillance of Aedes mosquitoes in a university campus in Kuala Lumpur, Malaysia. Tropical Biomedicine 26(2): Wan-Norafikah, O., Nazni, W.A., Noramiza, S., Shafa ar-ko ohar, S., Azirol-Hisham, A., Nor-Hafizah, R., Sumarni, M.G., Mohd- Hasrul, H., SofianAzirun, M. & Lee, H.L. (2010). Vertical dispersal of Aedes (Stegomyia) spp. In high-rise apartments in Putrajaya, Malaysia. Tropcial Biomedicine 27(3): Williams, C.R., Leach, K.J., Wilson, N.J. & Swart, V.R. (2008). The Allee effect in site choice behavior of egg-laying dengue vector mosquitoes. Tropical Biomedicine 25(2):